The present invention relates to a water conditioning apparatus for filtering certain undesirable materials from drinking water and, more particularly, to a small portable unit adapted to treat tap water by utilizing a semipermeable membrane to remove dissolved minerals.
The removal of dissolved minerals from water by reverse osmosis utilizing semipermeable membrane technology is well known in the art. Many types of undesirable dissolved solids which contribute to unpleasant taste, odor, hardness or the like may be selectively removed and retained on a semipermeable membrane through which the filtered water containing the remaining unobjectionable dissolved solids is caused to flow under pressure.
Apparatus of various types utilizing reverse osmosis to provide filtered water for home consumption are shown in the prior art. Typically, these filter units are adapted to be attached to a conventional household faucet to filter objectionable dissolved solids from tap water. One common construction utilizes a semipermeable membrane module in which a multiple layer member comprising a semipermeable membrane sheet between layers of a porous fabric and a plastic screen is spirally wound around a rigid, hollow cylindrical plastic tube. The module is appropriately sealed within a housing and unpurified water is forced to flow under pressure in an axial direction through the module where system pressure forces purified water radially through the membrane layers while retaining the selectively objectionable dissolved solids. The filtered purified water travels spirally toward the central product water tube which is provided with a series of radial holes allowing the filtered water to be collected in the center of the module for discharge from the unit. The retained dissolved solids pass axially through the module in a concentrated brine which is discharged to a drain or the like.
The construction of a multi-layer, spirally wound reverse osmosis module is described in detail in U.S. Pat. No. 3,504,796 (Bray). Reverse osmosis water treatment units utilizing a similar type of spirally wound filter module are also shown in U.S. Pat. Nos. 3,542,199 (Bray et al), 3,695,446 (Lyall et al), and 4,609,463 (Macevicz et al).
Many prior art filter units of the type described above are constructed in a manner to allow the filter module to be periodically removed and replaced. Because these filter units typically operate at relatively high pressures, appropriate sealing becomes critically important. The provision and maintenance of adequate seals has been a problem in some prior art devices, particularly those constructed with replaceable filter modules. In a typical construction, the water purification device must be sealed internally to assure that the unfiltered influent is forced under system pressure to pass through the multi-layer, spirally wound filter member and does not short circuit such passage by leaking past the interface between the interior product water tube and the upper and lower ends of the housing or the interface between the outer surface of the spirally wound filter member and the cylindrical inside surface of the housing. It is also important that the removable cover, providing access to the interior of the housing for filter module replacement, include an appropriate seal at its attachment interface with the housing.
The seal between the center product water tube and the lower and upper ends of the housing (the upper end typically comprising the inside surface of a removable cover) may utilize conventional O-rings placed in suitable circumferential grooves in one of the interfacing parts. Apart from the semipermeable membrane, most of the components of a filter unit are molded from plastic and, in accordance with conventional molding technology, many parts are formed with a longitudinal part line formed by the seam where the conventional mold halves join. The part line produces a small plastic ridge and, if the part line passes through a groove or other surface on which an O-ring is seated, small leaks past the O-ring may occur in service. Leaking may be further aggravated if the O-rings are periodically moved or otherwise disturbed as a result of removal of the filter module for replacement. To avoid this problem, some constructions utilize multiple O-ring seals at each component interface.
The so-called "brine seal" between the cylindrical OD of the filter module and the complimentary ID of the housing, as indicated, generally comprises a band of flexible sealing material attached to the OD of the filter module and compressed into engagement with the cylindrical ID of the housing when the filter module is installed therein. The band of flexible material may comprise an adhesive-backed plastic tape which is wrapped around the filter module. However, because of tee relatively fragile nature of the spirally-wound membrane assembly, it can be crushed or otherwise damaged by wrapping the brine seal tape too tightly. Another type of brine seal consists of a flexible rubber boot having a generally conical cross section which is wrapped around the filter module and includes an integral annular flange which extends radially toward the inside surface of the housing and axially in the direction of high system pressure. In operation, system pressure tends to force the annular flange into engagement with the inside surface of the housing, thereby enhancing the seal. However, the effective use of such a seal requires the accurate formation of interfacing components and fairly high dimensional tolerances. Defective or out of tolerance parts can result in leaking and the loss of the brine seal. Another problem common to all brine seals of the type shown in the prior art is that relative movement between the surfaces to be sealed as the filter module is inserted in the housing may distort or damage the sealing member. If the integrity of the seal is lost, it may not become apparent until the filter unit is closed and tested or put into service. In addition, anytime an untrained consumer must replace his own filter module, the problem of improper installation and subsequent loss of seal and leakage is more likely.